I am looking for a lightweight javascript library that allows the server to push update information to the client reliably and regularly. We use a fixed turn time of 300ms and often there are only about 20 bytes of changes. So doing polling using XMLHttpRequest would imply a huge overhead (3-way tcp handshake, http request headers, http response header).

There area number of alternatives, but they have limited browser support:

Java / Flash relays (requires the users to have those plugins installed)

Polling using XMLHttpRequest (huge overhead)

Is there a website which has recent information on which technology works in which browser? Are there javascript libraries which provide a common cross browser interface that hides the messy details? (Yes, i know that it still requires me to write multiple server sides, but that is rather easy. And more important it is easy to write automatic tests for the server sides).